Sign up to receive free email alerts when patent applications with chosen keywords are publishedSIGN UP

Abstract:

A method of preventive maintenance is disclosed for an aircraft. The
aircraft includes components, including items of equipment of the
aircraft and/or electronic modules and/or physical links. The lifetime
information for the components is known. The aircraft also includes means
for monitoring the components, a centralized maintenance system, and
means for estimating the life time of the components. The aircraft
carries out a set of functions, each being ensured by a chain of
components. The method comprises several steps including, a first step of
locating the degradations of the items of equipment, a second step making
it possible to allocate the located degradations to the various functions
of the aircraft, a third step of estimating the lifetime of the functions
identified in the second step, and a fourth step of formulating the
maintenance message constructed on the basis of the previous steps.

Claims:

1. A method of preventive maintenance for an aircraft, the aircraft
including:components, the components including items of equipment of the
aircraft and/or electronic modules and/or physical links, wherein the
lifetime information for the components is known, the aircraft further
including;means for monitoring the components,a centralized maintenance
system,a digital database,calculation means for computing a function for
estimating the life time of the components,an alarms manager,and display
means,and the aircraft carrying out a set of functions, each of the
functions being ensured by a chain of components, the method comprising
the steps of:locating, by the monitoring means, the degradations of at
least one item of equipment;allocating the located degradations to the
various functions of the aircraft on the basis of the database comprising
the list of components and the functional architecture of the
aircraft;estimating the lifetime of the functions identified in the
allocating step on the basis of the life time estimation function;
andformulating the preventive maintenance message, the latter being
constructed on the basis of the previous steps and of an alarms manager,
the message comprising degradation information linked with the various
functions of the aircraft as well as an estimate of the lifetime of at
least one function.

2. The method according to claim 1, wherein the degradations relate to the
environmental degradations pertaining to temperature, vibrations or
hygrometry, as well as the degradations of signals transmitted or
received by a component.

3. The method according to claim 1, wherein the degradations are located
by threshold overshoots, the thresholds being defined, according to the
nature of each of the degradations, by a predefined scale of numerical
values.

4. The method according to claim 1, further comprising collecting and
archiving the preventive maintenance messages, is carried out by the
centralized maintenance system.

5. The method according to claim 2, wherein a degradation information cue
generated by the centralized maintenance system, is transmitted to the
display means, the degradation information cue comprising the functional
degradation information and estimated lifetime information for at least
one function.

6. The method according to claim 1, wherein the estimated lifetime of a
function is the minimum lifetime of a set of components, each component
being indispensable to the realization of the function.

7. A maintenance device intended for a set of electronic or mechanical
items of equipment comprising a centralized maintenance system making it
possible to correlate the maintenance message formulated by the method of
claim 2 with fault reports.

8. The device according to claim 7, wherein an alarm message is generated
by the alarm manager destined for the pilot when a function has been
identified possessing a failure probability exceeding a predefined
threshold.

Description:

RELATED APPLICATIONS

[0001]The present application is based on, and claims priority from,
French Application Number 06 10732, filed Dec. 8, 2006, the disclosure of
which is hereby incorporated by reference herein in its entirety.

FIELD OF THE INVENTION

[0002]The present invention relates to the maintenance of a set of
equipment, such as the set of avionics equipment of an aircraft which
fulfils the various functions necessary for accomplishing a flight.

[0003]The methods and the device relate to the implementation of
preventive maintenance on the basis of proven degradations of the
aircraft's equipment. This preventive maintenance makes it possible to
schedule ground interventions with the best effectiveness and at the
least cost.

BACKGROUND

[0004]An aircraft comprises a large amount of equipment, of diverse
nature, mechanical, hydraulic, electrical or electronic, whose proper
operation is essential in the course of a flight.

[0005]To improve the degree of confidence accorded to this equipment,
monitoring of its proper operation is undertaken, as often as possible,
for each item. Monitoring generally comprises checking the fundamental
parameters and automatic or semi-automatic tests of proper operation.
Generally, a fault diagnosis is carried out and may lead to the emitting
of fault messages.

[0006]A monitoring and alarm function makes it possible to detect a
malfunction having an impact on the safety of the aircraft. A function of
this type, also called "Flight Warning" in the art, is present on certain
aircraft. A subfunction of the "Flight Warning", generally, named "Flight
Deck Effect" in the art, makes it possible to present these alarms to the
crew, these alarms referring to cockpit effects that may be interpreted
as anomalies by the pilot.

[0007]Additionally, a maintenance function is associated with the
monitoring function in order to diagnose faults and store them.

[0008]It is known by the name of BITE function, derived from the
abbreviation of the expression "Built In Test Equipment".

[0009]The BITE function of an item of equipment is taken on by electronics
which may be specific or shared with other functions of the item of
equipment considered. This electronics performs the software processing
required by the BITE function.

[0010]It comprises a more or less significant hardware part secured to the
item of equipment, with, at the minimum, in this hardware part, a
nonvolatile memory. Certain data are stored in the volatile memory,
including the breaching of standards by the monitored parameters, the
results of the tests, the fault diagnostic when it exists as well as the
fault messages emitted. The fault messages of the BITE functions of the
monitored equipment of an aircraft are addressed, by an airplane data
transmission link, to a centralizer item of equipment placed aboard the
aircraft so as to bundle together the various fault messages emitted.

[0011]Aboard recent aircraft, fault messages originating from the BITE
functions of the various items of equipment are consultable from the
flight deck. They are furthermore preprocessed, with a view to easing the
task of crews and maintenance personnel, by a specialized central
computer known by various terms such as CMC from the expression "Central
Maintenance Computer" or else CFDIU from the expression "Centralized
Fault Display Interface Unit".

[0012]This central maintenance computer is accessible by the crew through
an interface with keyboard and screen which may be that known by the
abbreviation MCDU derived from the expression "Multipurpose Control
Display Unit" but which may also be a portable computer of the PC kind
attached by a disconnectable data link which does or does not utilize the
airplane bus.

[0013]Its main function is to effect, in real time or at the end of a
flight, a diagnostic of the general situation of the aircraft. This
diagnostic is carried out on the basis of a summary of the fault messages
received from the various items of equipment of the aircraft.

[0014]II also fulfils other functions such as: [0015]correlation of the
fault messages received with the alarms received at the flight deck
level; [0016]running of particular tests on the items of equipment,
conducted on request, by an operator intervening from the keyboard-screen
interface giving access to the central maintenance computer;
[0017]drafting of a "post-flight" report, known by various terms such as
PFR or LLR for "Post Flight Report" or "Last Leg Report". This report is,
generally, carried out for the maintenance teams on the ground.

[0018]The latter function which consists in providing a "post-flight"
report makes it possible to ease the work of the ground maintenance crew.
It comprises a log of the fault messages emitted by the various items of
equipment of the aircraft and alarms presented to the crew as well as the
summary of the fault messages made as a last resort and more generally,
all the information on the operating states of the equipment. The
information featuring in this report results from automatic exploitation
of the equipment fault messages or remarks by the crew.

[0019]The faults are generally correlated with the equipment failure
probability. This failure probability is estimated on the basis of a
reliability model and is stored in a static manner.

[0020]This correlation makes it possible to plan anticipated or preventive
maintenance actions on the corresponding items of equipment.

[0021]The logical chain for deciding the maintenance actions results from
the noting of a proven fault and then its location and finally a
formulated diagnostic.

[0022]Additionally, more and more data are being monitored around avionics
equipment, such as vibrations, electromagnetic and thermal signatures and
other data which make it possible to reconstitute the immediate
environment of the computer. These data do not systematically generate
proven faults.

[0023]Certain monitoring systems analyse the error rate or the number of
lost frames which make it possible to identify not a fault but a possible
degradation of the wiring. It is considered that this monitoring and the
analysis of the degradations of an item of equipment may lead to a
prognosis being carried out on the airplane's data network.

[0024]A prognosis carried out on engines exists today. Prognoses are
evaluated on certain items of equipment, notably those named ACMS, the
acronym standing for Aircraft Condition Monitoring System. The engine
parameters, such as the temperatures or vibrations, for example, are
recovered and monitored. Certain breaches of thresholds (or overshoots),
for example, make it possible to trigger alarms advocating intervention
actions.

[0025]On the other hand, the monitoring of these fault generating
degradations is not correlated with the functions of the system. No
functional analysis is carried out on the basis of the degradations
detected. Moreover, the degradation information is processed without
considering the reliability model of the functions, and this could make
it possible to provide a preventive maintenance report.

[0026]Moreover, the analysis of the degradations is not generalized to all
the equipment and is not analysed jointly with the functional
architecture of an aircraft.

SUMMARY OF THE INVENTION

[0027]An aim of the invention is notably to alleviate the aforesaid
drawbacks. For this purpose, the object of the invention is, in regard to
the noted and analysed degradations of an aircraft, to centralize them by
way of a function, named "Centralized Prognostic System"

[0028]On the basis of a known functional architecture of the aircraft and
of the relation which links a function of the system to the equipment, an
estimate of the lifetime of the function is calculated as a function of
the lifetime of the components of the aircraft and of the degradations of
the components, the said components comprising the various items of
equipment and the physical linkups linking them.

[0029]Advantageously, the method of preventive maintenance for aircraft,
the said aircraft comprising: [0030]components, the said components
comprising items of equipment of the aircraft and/or electronic modules
and/or physical links, the lifetime information for the components being
known; [0031]means for monitoring the components; [0032]a centralized
maintenance system (CMC); [0033]a digital database; [0034]calculation
means for computing a function for estimating the life time of the
components; [0035]an alarms manager; [0036]and display means; [0037]and
carrying out a set of functions, each of the functions of the aircraft
being ensured by a chain of components.

[0038]The method according to the invention comprises: [0039]1. A first
step of locating, by the monitoring means, the degradations of at least
one item of equipment; [0040]2. A second step making it possible to
allocate the located degradations to the various functions of the
aircraft on the basis of the database comprising the list of components
and the functional architecture of the aircraft; [0041]3. A third step of
estimating the lifetime of the functions identified in the second step on
the basis of the life time estimation function; [0042]4. A fourth step of
formulating the preventive maintenance message, the latter being
constructed on the basis of the previous steps and of an alarms manager,
the said message comprising degradation information linked with the
various functions of the aircraft as well as an estimate of the lifetime
of at least one function.

[0043]Advantageously, the degradations relate to the environmental
degradations pertaining to temperature, vibrations or hygrometry, as well
as the degradations of signals transmitted or received by the components.

[0044]Advantageously, the degradations are located by threshold
overshoots, the said thresholds being defined, according to the nature of
each of the degradations, by a predefined scale of numerical values.

[0045]Advantageously, a fifth step of collecting and archiving the
preventive maintenance messages is carried out by the centralized
maintenance system.

[0046]Advantageously, a degradation information cue, generated by the
centralized maintenance system, is transmitted to the display means, the
said degradation information cue comprising the functional degradation
information and estimated lifetime information for at least one function.

[0047]Advantageously, the estimated lifetime of a function is the minimum
lifetime of a set of components, each component being indispensable to
the realization of the function.

[0048]Advantageously, an alarm message is generated by the alarm manager
for the pilot indicating a probability of loss of at least one function,
said message being used to identify the status of the aircraft before
take off.

[0049]Advantageously, the status of the aircraft comprises, notably,
information relating to the number of components fulfilling a function,
the minimum number of components required to ensure the function.

[0050]Advantageously, the maintenance device is intended for a set of
electronic or mechanical items of equipment comprising a centralized
maintenance system, the said system making it possible to correlate the
maintenance message formulated by the method described above with fault
reports.

[0051]Still other objects and advantages of the present invention will
become readily apparent to those skilled in the art from the following
detailed description, wherein the preferred embodiments of the invention
are shown and described, simply by way of illustration of the best mode
contemplated of carrying out the invention. As will be realized, the
invention is capable of other and different embodiments, and its several
details are capable of modifications in various obvious aspects, all
without departing from the invention. Accordingly, the drawings and
description thereof are to be regarded as illustrative in nature, and not
as restrictive.

BRIEF DESCRIPTION OF THE DRAWINGS

[0052]The present invention is illustrated by way of example, and not by
limitation, in the figures of the accompanying drawings, wherein elements
having the same reference numeral designations represent like elements
throughout and wherein:

[0053]FIG. 1: The various steps of the method according to the invention;

[0055]FIG. 3: Allocation of the functions to the components of the
sub-system.

PREFERRED EMBODIMENTS OF THE INVENTION

[0056]The method according to the invention comprises several steps making
it possible to construct, on the basis of the degradations of the
components of the aircraft, a preventive maintenance message relating to
the possible functional losses of the aircraft.

[0057]A set of items of equipment carrying out an aircraft level function
is called a "system" or "sub-system" of the aircraft. For example, the
aircraft can be considered as a system.

[0058]Additionally, any item of equipment of the aircraft or a part of an
item of equipment of the aircraft, such as a module or an electronic card
or else a physical link connecting two other components, is called a
"component".

[0059]The physical links can be of various kinds, such as physical links,
electrical links, optical links, hydraulic or pneumatic links.

[0060]Finally, it is considered that the aircraft comprises a set of
functions and sub-functions, the latter being ensured by a chain of
components. There exist several types of functions.

[0061]High-level functions can be, for example, the "aircraft guidance"
function or the "piloting" function. Low-level functions can be, for
example, the function "generate meteorological images" or the function
"transfer altimetry data from the antenna to the display means".

[0062]There exist functions of a vital nature for the aircraft and others
that are less critical for carrying out the main missions of an aircraft.

[0063]The "functional architecture" is defined subsequently as the set of
relations linking the various functions of the aircraft.

[0064]FIG. 1 represents the chaining of the various steps of the method.
On the basis of monitoring the degradations of the aircraft components, a
first step is carried out so as to locate degradations in the aircraft.
Once the various degradations have been located, a second step of
functional allocation of the degradations to the functions is carried
out. This step is performed on the basis of a functional architecture of
the aircraft. In a third step, the reliability model of the components is
extended to the functions of the aircraft to estimate the lifetime of
certain functions, notably those to which the degradations relate. A
fourth step makes it possible to formulate a preventive maintenance
message so as to provide the centralized maintenance system with various
preventive maintenance alarms.

[0065]The first step of locating the degradations, on the basis of
monitoring means, makes it possible to identify the degradations of an
item of equipment and to collect them. A function, called "Centralized
Prognostic System", makes it possible to centralize the degradation
information.

[0066]There exist several types of degradations measurable by known
analysis means.

[0067]A first type of degradation is detected by environmental constraint
measurement mechanisms. In this case the degradations are, notably,
tagged by threshold overshoots for example. This may concern, for
example, degradation information pertaining to the temperature, to the
vibrations or else to the hygrometry of an item of equipment.

[0068]A second type of degradation relates to the measurements of the
quality and/or quantity of digital or analogue signals. The number of
frames lost in a link, the bit error rates of a data transfer or else the
ratios of the level of a signal to the noise of an emit or a receive are
various examples of degradations of this type.

[0069]The results are transmitted to the "Centralized Prognostic System"
function and analysed so as to formulate, optionally, a report relating
to the degradations, their frequency, their amplitude and their
inter-consistency. Moreover, an analysis of the degradation of a
component and of the properties of the component itself is performed.

[0070]Notably, an analysis consists in associating the lifetime of the
component with each component of the system.

[0071]The Centralized Prognostic System function collects in a database
for example the list of components, their lifetime and the degradations
noted over a determined period.

[0072]A second step consists, on the basis of the known functional
architecture of the system, the aircraft for example, in correlating the
components with the various functions.

[0073]On the basis of the knowledge of the airplane configuration, the
relation between the functions or sub-functions of the system and the
items of equipment and/or the physical linkups of which it consists are
available.

[0074]The airplane configuration is, generally, available in a centralized
function for managing the airplane configuration or directly in the
centralized maintenance function.

[0076]Generally, an airplane sub-system can be considered to be a set of
means each being a component, that is to say an item of equipment or a
sub-item of equipment for example.

[0077]FIG. 2 represents the various components of this sub-system by
independent blocks. Each of the components is an item of equipment. The
arrows represent in this example the direction of data captures and of
their processing. The following means are considered in this example:

[0078]means for capturing physical data, denoted M1;

[0079]means for processing and analysing these data, denoted M2;

[0080]means for transmitting these data, denoted M3;

[0081]control means, denoted M4, comprising an actuator.

[0082]viewing means, denoted M5, and finally;

[0083]A certain number of functions and sub-functions are ensured by this
sub-system. Each of these functions is not ensured by a single item of
equipment.

[0084]Three functions of this sub-system are considered, the three
functions supported by the aforesaid sub-system are denoted F1, F2 and
F3. F3 can be a generation of icons represented on the screen on the
basis of the captured data, F2 a guidance setpoint for the sensors, and
finally F1 a generation of frames.

[0085]FIG. 3 represents an array corresponding to the relations between
the functions and the aforesaid means. Each of these functions is carried
out through the assistance of several components, like the electronic
equipment customarily integrated in avionics.

[0086]For example, row number 1 of FIG. 3 specifies the relations between
the function F1 which is carried out on the basis of the means M1, M2 and
M3. A cross is represented in the array when a relation exists.

[0087]A third step consists in combining the allocation of the functions
to each component with the estimated lifetimes of each of these
components.

[0088]The estimated lifetime of a component is called, according to the
terminology of the art, "time to live", it is denoted TTL.

[0089]There exist various ways to calculate the lifetimes of each of the
functions. An exemplary calculation consists in determining the minimum
of the lifetime of the components, each of the said components
contributing to carrying out the function. This example does not restrict
the scope of the method according to the invention.

[0090]The lifetime of each function is, therefore, determined by the most
limiting lifetime of the components which contribute to carrying out the
function.

[0091]The respective lifetimes of the means M1, M2, M3, M4, M5 are denoted
TTLM1, TTLM2, TTLM3, TTLM4, TTLM5. In this
example, the following convention is written, following a prior
calculation of each of the estimated lifetimes of each of the items of
equipment:

TTLM1>TTLM2>TTLM3>TTLM4>TTLM5

The lifetimes of the functions F1, F2, F3 are denoted TTLF1,
TTLF2, TTLF3 respectively. The following relations are
therefore obtained:

TTLF1=Minimum(TTLM1,TTLM2,TTLM3)=TTLM3

TTLF2=Minimum(TTLM1,TTLM2,TTLM4)=TTLM4

TTLF3=Minimum(TTLM2,TTLM5)=TTLM5

[0092]Additionally, any system or sub-system of an aircraft can be
processed like the example of the sub-system above. The method according
to the invention relates to all the systems included in an aircraft,
including the aircraft system itself.

[0093]The above case of realization does not restrict the scope of the
method according to the invention, but constitutes a case of realization
applied to a sub-system of the aircraft.

[0094]A last step of constructing the maintenance message makes it
possible to inform the maintenance operator and possibly the pilot, by
means of alarms, generated by way of an alarm manager, of the possible
loss of certain functions due to certain degradations. The possible loss
is assessed by analysing the calculated lifetime of each function.

[0095]In order to carry out the latter step, the maintenance message uses
the current means which generate the proven faults in order to make it
possible to construct functional loss alarms identically.

[0096]The logic for emitting these alarms is, generally, centralized in
the alarms management centre, also called "Flight Warning" in the art.
Some of them are emitted to the viewing means, so as to provide the pilot
with a preventive functional loss information cue.

[0097]For example a maintenance message can be supplemented with possible
information regarding functional degradations that are imminent or have a
longer timescale so as to enable the pilot to decide whether or not the
aircraft should take off. An estimated lifetime of a functional
degradation may be provided to the pilot, as well as an assessment of the
significance of the seriousness of the degradation.

[0098]The maintenance message thus formulated can be for example: "loss of
the function F2 in 4 months", thus taking into account the noted
degradation of the component (components) as well as the estimated
lifetime of this (these) component (components).

[0099]In the latter case, the message is an input datum for what is called
the "Minimum Equipment List", denoted MEL. This list identifies the
status of the aircraft so as to permit or not permit the flight. Notably
this list provides a list of the restrictions and limitations of uses
according to the messages or alarms which are dispatched to the MEL. The
MEL also gives the number of elements fulfilling a function, the minimum
number of elements required, possibly any remarks or else exceptions.

[0100]Thus, the method according to the invention allows [0101]the
maintenance operator to clearly identify a degradation and the impact of
this degradation on the functions of the aircraft. It is, hence, possible
to best schedule the next maintenance operations and to improve the times
during which the aircraft is grounded; [0102]the pilot to ascertain in a
preventive manner a functional state of the aircraft when required and
possibly to monitor the MEL which can comprise prognoses of functional
degradations of the aircraft.

[0103]It will be readily seen by one of ordinary skill in the art that the
present invention fulfils all of the objects set forth above. After
reading the foregoing specification, one of ordinary skill in the art
will be able to affect various changes, substitutions of equilvalents and
various aspects of the inventions as broadly disclosed herein. It is
therefore intended that the protection granted hereon be limited only by
the definition contained in the appended claims and equivalent thereof.